1. Field of the Invention
The present invention relates to a receiver, which includes a phased array antenna section and performs demodulation in accordance with the direct conversion method.
2. Description of the Related Art
In a conventional receiver including a phased array antenna, RF signals received by antenna elements are combined as they are, and demodulation is performed based on the combined signal.
Also, a conventional demodulator is, for example, of the direct conversion type using a mixer and a local signal.
Such a receiver including a phased array antenna, however, has a disadvantage in that since RF signals received by antenna elements are combined as they are, the amplitudes of the signals received by the antenna elements are uncertain and directivity control required in, e.g., the so-called beamformer, is difficult to perform.
Further, the demodulation method using a mixer has a difficulty in realizing a wider band and requires a high local level to be applied to the mixer. In addition, since the mixer is supplied with a high local power and is in a nonlinear operating state, a disadvantage occurs in that it is difficult to perform demodulation with a low distortion.
In view of the state of the art set forth above, it is an object of the present invention to provide a receiver, which can reliably recognize the amplitudes of signals received by antenna elements, can easily perform directivity control, and can realize demodulation over a wider band with a low distortion.
To achieve the above object, a receiver according to one aspect of the present invention comprises a phased array antenna section including a plurality of antenna elements each receiving a radio signal, a plurality of phase varying circuits for controlling phases of the respective signals received by the antenna elements to desired different phases, and a signal combiner for combining output signals of the plurality of phase varying circuits; a direct conversion demodulating section including a local signal generating circuit for generating a local signal of predetermined frequency, a generating unit for receiving a combined received signal, which is supplied from the signal combiner of the phased array antenna section, or a calibration signal and the local signal from the local signal generating circuit, for generating two signals having a phase difference therebetween based on at least one of the signals received by the generating unit, and for outputting at least one signal, at least one power detecting circuit for receiving the signal outputted from the generating unit and detecting a level of the signal received from the same, and a conversion circuit for, in a reception mode, converting the output signal of the power detecting circuit to a plurality of signal components, which are contained in the received signal or the local signal, based on set values of circuit parameters, and for, in a non-reception mode in which signals are not received, determining the values of the circuit parameters based on the output signal of the power detecting circuit and then correcting the circuit parameters to the determined values; and a switch circuit for, in the reception mode, applying the combined received signal outputted from the signal combiner of the phased array antenna section to the direct conversion demodulating section, and for, in the non-reception mode, applying the calibration signal to the direct conversion demodulating section instead of the combined received signal outputted from the signal combiner of the phased array antenna section.
Also, a receiver according to another aspect of the present invention comprises a phased array antenna section including a plurality of antenna elements for receiving a radio signal, a plurality of phase varying circuits for controlling phases of the respective signals received by the antenna elements to desired different phases, and a signal combiner for combining output signals of the plurality of phase varying circuits; a direct conversion demodulating section including a local signal generating circuit for generating a local signal of predetermined frequency, a generating unit for receiving a combined received signal, which is supplied from the signal combiner of the phased array antenna section, or a calibration signal and the local signal from the local signal generating circuit, for generating two signals having a phase difference therebetween based on at least one of the signals received by the generating unit, and for outputting at least one signal, at least one power detecting circuit for receiving the signal outputted from the generating unit and detecting a level of the signal received from the same, and a conversion circuit for, in a reception mode, converting the output signal of the power detecting circuit to a plurality of signal components, which are contained in the received signal or the local signal, based on set values of circuit parameters, and for, in a non-reception mode in which signals are not received, determining the values of the circuit parameters based on the output signal of the power detecting circuit and then correcting the circuit parameters to the determined values; and a switch control section for, in the non-reception mode, applying the local signal from the local signal generating circuit of the direct conversion demodulating section to one of the plurality of phase varying circuits of the phased array antenna section instead of the received signal from the antenna element corresponding to the one phase varying circuit, for setting a phase of the local signal, which is inputted to the one phase varying circuit, to a predetermined phase, and for applying the signal having been set to the predetermined phase, as the calibration signal, to the generating unit of the direct conversion demodulating section instead of the combined received signal outputted from the signal combiner of the phased array antenna section.
Preferably, the switch control section includes a control circuit for, at least in the non-reception mode, controlling the one phase varying circuit to set the phase of the local signal inputted thereto to be different from the phase of the local signal inputted to the generating unit.
Preferably, the switch control section comprises a first switch circuit having a first terminal connected to an output line of the antenna element corresponding to the one phase varying circuit, a second terminal connected to a local signal output terminal of the local signal generating circuit, and a third terminal connected to an input terminal of the one phase varying circuit, the first switch circuit selectively connecting the third terminal to the first terminal or the second terminal in response to a control signal; a second switch circuit having a first terminal connected to one input terminal of the signal combiner, a second terminal, and a third terminal connected to an output terminal of the one phase varying circuit, the second switch circuit selectively connecting the third terminal to the first terminal or the second terminal in response to the control signal; a third switch circuit having a first terminal connected to an output terminal of the signal combiner, a second terminal connected to the second terminal of the second switch circuit, and a third terminal connected to an input terminal of the generating unit, the third switch circuit selectively connecting the third terminal to the first terminal or the second terminal in response to the control signal; and a control circuit for, in the reception mode, controlling each of the first switch circuit, the second switch circuit and the third switch circuit by the control signal such that the third terminal is connected to the first terminal, and for, in the non-reception mode, controlling each of the first switch circuit, the second switch circuit and the third switch circuit by the control signal such that the third terminal is connected to the second terminal.
Preferably, at least in the non-reception mode, the control circuit controls the one phase varying circuit to set the phase of the local signal inputted thereto to be different from the phase of the local signal inputted to the generating unit.
Preferably, the local signal generating circuit sets a level of the local signal based on an output signal of the conversion circuit.
Preferably, the direct conversion demodulating section further includes a reproducing circuit for reproducing a carrier signal, which has the same frequency as that set by the local signal generating circuit, based on converted signals from the conversion circuit.
According to one aspect of the present invention, in the reception mode, the signals received by the antenna elements of the phased array antenna section pass the corresponding phase varying circuits, and are combined by the signal combiner.
At this time, the phase varying circuits of the phased array antenna section are controlled so as to change the phases of the received signals at values different from one another.
The combined received signal combined by and outputted from the signal combiner is applied to the first input terminal of the generating unit of the direct conversion demodulating section.
Also, the local signal of predetermined frequency generated from the local signal generating circuit is applied to the second input terminal of the generating unit.
The generating unit generates at least two signals having a phase difference between them based on the combined received signal and the local signal, and then supplies the combined received signal, the local signal and the generated signals to the power detecting circuit.
The power detecting circuit detects the signal level i.e., the amplitude component, of the input signal, and supplies a detected signal to the conversion circuit.
The conversion circuit demodulates the input detected signals to obtain signal components, i.e., an in-phase signal I and a quadrature signal Q, which are contained in the received signal, based on the values of circuit constants (parameters) including circuit parameters of the generating unit.
On the other hand, when executing the calibration to calculate the values of the circuit parameters, i.e., in the non-reception mode, the calibration signal is supplied to the first input terminal of the generating unit instead of the combined received signal.
In this case, the local signal generated by the local signal generating circuit is inputted to one of the phase varying circuits.
The local signal is also supplied to the second input terminal of the generating unit.
In the one phase varying circuit, the calibration signal having a phase different from that of the local signal, inputted to the generating unit, is generated in response to the control signal from the control circuit, and then supplied to the first input terminal of the generating unit through the second switch circuit and the third switch circuit.
The generating unit generates at least two signals having a phase difference between them based on the calibration signal and the local signal, and then supplies the calibration signal, the local signal and the generated signals to the power detecting circuit.
The power detecting circuit detects the signal level i.e., the amplitude component, of the input signal, and supplies a detected signal to the conversion circuit.
In the conversion circuit, the values of desired circuit parameters are calculated with predetermined simultaneous equations by comparing two signals having different phases with each other. The circuit parameters having been set so far are corrected in accordance with the calculated circuit parameters.
After that time, the conversion in the reception mode is executed using the corrected circuit parameters.
According to another aspect of the present invention, in the reception mode, the first switch circuit, the second switch circuit and the third switch circuit of the switch control section are each controlled by the control signal from the control circuit such that the third terminal is connected to the first terminal.
Upon the changeover of the switch circuits, the input terminal of the one phase varying circuit is connected to the output line of the corresponding antenna element, the output terminal of the one phase varying circuit is connected to one input terminal of the signal combiner, and the output terminal of the signal combiner is connected to the input terminal of the generating unit.
With that arrangement, in the reception mode, the signals received by the antenna elements of the phased array antenna section pass the corresponding phase varying circuits, and are combined by the signal combiner.
At this time, the phase varying circuits of the phased array antenna section are controlled so as to change the phases of the received signals at values different from one another.
The combined received signal combined by and outputted from the signal combiner is applied to the first input terminal of the generating unit of the direct conversion demodulating section.
Also, the local signal of predetermined frequency generated from the local signal generating circuit is applied to the second input terminal of the generating unit.
The generating unit generates at least two signals having a phase difference between them based on the combined received signal and the local signal, and then supplies the combined received signal, the local signal and the generated signals to the power detecting circuit.
The power detecting circuit detects the signal level i.e., the amplitude component, of the input signal, and supplies a detected signal to the conversion circuit.
The conversion circuit demodulates the input detected signals to obtain signal components, i.e., an in-phase signal I and a quadrature signal Q, which are contained in the received signal, based on the values of circuit constants (parameters) including circuit parameters of the generating unit.
On the other hand, when executing the calibration to calculate the values of the circuit parameters, i.e., in the non-reception mode, the first switch circuit, the second switch circuit and the third switch circuit of the switch control section are each controlled by the control signal from the control circuit such that the third terminal is connected to the second terminal.
Upon the changeover of the switch circuits, the local signal output terminal of the local signal generating circuit is connected to the input terminal of the one phase varying circuit, and the output terminal of the one phase varying circuit is connected to the input terminal of the generating unit.
An output signal of the one phase varying circuit is supplied to the first input terminal of the generating unit instead of the combined received signal.
In this case, the local signal generated by the local signal generating circuit is inputted to the one phase varying circuits.
The local signal is also supplied to the second input terminal of the generating unit.
In the one phase varying circuit, the calibration signal having a phase different from that of the local signal, inputted to the generating unit, is generated in response to the control signal from the control circuit, and then supplied to the first input terminal of the generating unit through the second switch circuit and the third switch circuit.
The generating unit generates at least two signals having a phase difference between them based on the calibration signal and the local signal, and then supplies the calibration signal, the local signal and the generated signals to the power detecting circuit.
The power detecting circuit detects the signal level i.e., the amplitude component, of the input signal, and supplies a detected signal to the conversion circuit.
In the conversion circuit, the values of desired circuit parameters are calculated with predetermined simultaneous equations by comparing two signals having different phases with each other. The circuit parameters having been set so far are corrected in accordance with the calculated circuit parameters.
After that time, the conversion in the reception mode is executed using the corrected circuit parameters.
With the features set forth above, the present invention can provide the following advantages. Directivity of a phased array antenna can be controlled as desired, and the amplitudes of the signals received by the antenna elements can be can be always confirmed without becoming uncertain.
Also, since the receiver uses a multi-port demodulator including the power detecting circuit, it can easily realize demodulation over a wider band and has good adaptability for software radio communications that require multiband or wideband characteristics. While recent radio communications have a tendency to employ higher frequency as the carrier frequency, the receiver is also adaptable for such a demand for the use of higher frequency.
Further, since the power detecting circuit operates in a linear range in the multi-port demodulation, a low-power local signal can be used to perform demodulation with a low distortion.
In addition, according to the present invention, it is possible to prevent an increase in the receiver size and to realize a cost reduction.
Moreover, since the receiver includes the phase varying circuit which also functions as a calibration circuit, frequency changes, temperature-dependent changes, and changes over time of internal parameters of a multi-port direct conversion circuit can be compensated for through self-calibration.